'He called us rats, but he is the one hiding. We shall hang them all together. . .'

The machine-gun fire cut across the patriotic songs belting out of the ghetto-blaster, long raking bursts sending the rebel fighters scrambling for cover. One, little more than a boy, fell to the ground, blood streaming from his face as he desperately held out his hands for two friends to drag him away.

The attack in the Gargaresh district was one of many skirmishes, short and brutal exchanges, in Tripoli on the day Muammar Gaddafi finally fell from power. The revolutionaries had been greeted with celebration by many residents as they had come into the Libyan capital during the night.

Green Square, the heart of the city, had for a while been the scene of a spontaneous party. But that had broken up amid sniper attacks. The morning was tense beneath the bonhomie, and by the afternoon a rolling battle was unfolding in the centre of the city.

Standing on the terrace of the Corinthia, a five-star hotel that was used by the regime for guests, I could see gunmen on the 12th floor of a building firing down towards the port where the opposition fighters had set up a checkpoint. The response came in the shape of mortars and rocket-propelled grenades, some landing uncomfortably close. The few foreign guests at the hotel had thought yesterday would be the day they would escape their enforced stay; that hope evaporated with the gunfire.

Plumes of smoke rose over the Bab al-Aziziya, Colonel Gaddafi's base, where, ran one line of rumour, he may be secreted in a bunker. The complex had been under disorganised attack from the rebels from the early hours. "Judgement Day for Gaddafi" said a banner being waved. News had started arriving in excited shouts of how two of the dictator's sons – Saif al-Islam and Mohammed – had already been captured. The Prime Minister, Al Baghdadi Ali al-Mahmoudi, was under siege by supporters of the revolution at a hotel in the Tunisian city of Djerba while trying to escape, another bulletin ran.

"Gaddafi called us rats, but he is the one hiding in a hole" shouted Osama Mohammed Sattar, a leader of the Shabab youth volunteers, letting off a volley of shots from his Kalashnikov. "We shall hang all of them together when we catch him." But capital punishment has been abolished in Libya, I pointed out. "There are men's laws and God's law," came the answer with grim relish.

The regime's official spokesman, Moussa Ibrahim, had claimed that there "would be a massacre, hundreds would be murdered" when the rebels took over Tripoli. The charge, made by the apologist-in-chief for a regime which had practised mass slaughter, has been unfounded. But there have been individual acts of retribution, arbitrary and vicious, on helpless victims.

At the Maghrabi Arab Village, built for expatriates working in the petroleum industry, two young black men squatted on the ground, terrified, their hands tied behind their backs, guns held to their heads. I was told by one of the rebels that they were Mohammed Salou Mohammed, and Zait Abidan Ali, from Chad. Both had confessed to being snipers working for Colonel Gaddafi. Did they really admit to that? The fighter, looking uncomfortable, insisted that was indeed the case. Zait Abidan Ali started to say they just worked at the place. He was kicked in the chest by a fat man in torn British Army fatigues who said he was a commander and ordered me to leave.

The repeated cases of men from sub-Saharan Africa being lynched by rebels on the pretext that they were regime mercenaries has been one of the most disturbing aspects of the revolution. My colleagues and I had witnessed some of these killings while with the rebel forces in eastern Libya. Human-rights groups had protested and the opposition administration, the Transitional National Council (TNC), had promised action. As the men were led away, another fighter, Nasr Al-Sabri, said: "I am sorry about this, but this is a difficult time and people are angry. We have lost people to snipers in the last few days. But I will try to make sure that these men are dealt with properly. This is unusual, you can see how glad the people of Tripoli are to see us."

At a nearby alleyway where I had stopped after more shots were fired, Khalid bin Abdus spoke in a quiet voice about his imprisonment in the Abu Salem jail in Tripoli, a place of fear where 1,200 inmates were massacred in 1996. The 28-year-old sign painter walked with a limp. "A souvenir from Gaddafi," he said, laughing. "It is the result of daily beatings; it was meant to teach us never to cross him again. I was lucky, my brother disappeared after being arrested. We were told four years later that he had been killed."

Nabil Bin Munir, 37, an electrical engineer, added: "You did not even have to go to prison to be oppressed. It is difficult for people from the outside to understand what it is like to live in a state where they monitor everything you do, what you think. When I was at university I used to share a room with other students. I would be afraid that I would say something in my sleep which could be disloyal by someone. We had 41 years of this; generations grew up being afraid."

Seventeen-year-old Khatan Jarafa fought to avoid that fate. He had run away three months ago to join the rebels in the Nafusa Mountains. A slight, bespectacled figure in a Manchester United shirt, he flinched at the sound of every gunshot as he described how worried his mother, Sabah, had been when he left for the revolution. But now Khatan was worried about her. "She is a judge. She was always fair with people, but now criminals may come and say false things about her," he said. "My father and I are very concerned about this."

His friend Adem Mukhtar, 19, and also a member of the Shabab, tried to reassure him: "We want everyone to get on together. That is what this is about."